Editing Gram-negative bacteria (section)

== Characteristics ==
[[File:Gram negative cell wall.svg|thumb|500px|right|Gram-negative (LPS-diderm) [[cell wall]] structure]]
[[File:Gram-Cell-wall.svg|thumb|right|[[Gram-positive]] and -negative [[bacteria]] are differentiated chiefly by their [[cell wall]] structure]]

Conventional gram-negative (LPS-diderm) bacteria display {{nowrap|the following characteristics}}:{{cn|date=July 2022}}
* An inner [[cell membrane]] is present ([[cytoplasm]]ic)
* A thin [[peptidoglycan]] layer is present (this is much thicker in gram-positive bacteria)
* Has [[Bacterial outer membrane|outer membrane]] containing [[lipopolysaccharide]]s (LPS, which consists of [[lipid A]], core [[polysaccharide]], and [[O antigen]]) in its outer leaflet and [[phospholipid]]s in the inner leaflet
* [[Porin (protein)|Porins]] exist in the outer membrane, which act like pores for particular molecules
* Between the outer membrane and the [[Cell membrane|cytoplasmic membrane]] there is a space filled with a concentrated gel-like substance called [[periplasm]]
* The [[S-layer]] is directly attached to the outer membrane rather than to the [[peptidoglycan]]
* If present, [[flagella]] have four supporting rings instead of two
* [[Teichoic acid]]s or [[lipoteichoic acid]]s are absent
* [[Lipoprotein]]s are attached to the polysaccharide backbone
* Some contain [[Braun's lipoprotein]], which serves as a link between the outer membrane and the peptidoglycan chain by a covalent bond
* Most, with few exceptions, do not form [[Endospore|spores]]

However, the LPS-diderm group (corresponding to kingdom [[Pseudomonadati]], formerly 'Hydrobacteria') is not the only type of bacteria that stain negative.<ref name="valid-dom-kingdom">{{cite journal |last1=Göker |first1=Markus |last2=Oren |first2=Aharon |title=Valid publication of names of two domains and seven kingdoms of prokaryotes |journal=International Journal of Systematic and Evolutionary Microbiology |date=22 January 2024 |volume=74 |issue=1 |doi=10.1099/ijsem.0.006242|pmid=38252124 }}</ref> ''[[Mycobacterium]]'' (or rather most of [[Mycobacteriales]]), which does not belong in the group, have independently evolved an outer cell membrane, with a cell wall made of [[mycolic acid]].<ref name=Gupta19myc>{{cite journal |last1=Gupta |first1=Radhey S. |title=Commentary: Genome-Based Taxonomic Classification of the Phylum Actinobacteria |journal=Frontiers in Microbiology |date=22 February 2019 |volume=10 |page=206 |doi=10.3389/fmicb.2019.00206 |quote=Mycolic acids are important constituents of the cell envelopes of most members.|doi-access=free |pmid=30853945 |pmc=6395429 }}</ref> This gives it very different structure and features.<ref name="Desvaux et al., 2009"/><ref name="Sutcliffe, 2010"/><ref name="Guptac"/><ref name="pmid19667386">{{cite journal|vauthors=Marchandin H, Teyssier C, Campos J, Jean-Pierre H, Roger F, Gay B, Carlier JP, Jumas-Bilak E |title=Negativicoccus succinicivorans gen. nov., sp. nov., isolated from human clinical samples, emended description of the family Veillonellaceae and description of Negativicutes classis nov., Selenomonadales ord. nov. and Acidaminococcaceae fam. nov. in the bacterial phylum Firmicutes |journal=Int. J. Syst. Evol. Microbiol. |volume=60 |issue=Pt 6 |pages=1271–9 |date=June 2010 |pmid=19667386 |doi=10.1099/ijs.0.013102-0|doi-access=free }}</ref>